Rifled gun barrel



Aug. 13, 1963 T. R. ROBINSON, JR 3,100,358

RIFLED GUN BARREL Original Filed May 13, 1953 3 Sheets-Smet 5 INVENTOR gmwg ATTORNEY U t s atent O" essense f] annan GUN hanteer Thomas R. Robinson, r., New Haven, Cohn, to' The Merlin firearms 'Company, New Haven, Cohn., a

t corporation of Connecticut p continuation ei application Ser., No. 354,712, May 13, 1953. 'flits appiication Nov. 27,?1959, SenNo. 355,331

n l ZCiaims. (Ci. 42--78) This invention relates to rifled gun barrels and more particuiarly to a barrel having a new, novel, .and advantageous type' ofriflingyand to a method of eiecting such rilling, the barrel so made possessing to a degree not `hitherto attained the attributes of low cost of manufacture, extreme accuracy of performance and long useful life. The present application is a continuahon of `my ap- `piication,Serial`No. 354,712, filed May 13, 1953, now

cutting of each groove. r i r For example, a .30 caliber rifle may have from four to six of such grooves Which may be cut to a depth of .004 in.

This means that the bore diameter ofthe barrel across the` v lands between the grooves is .308 in., while the groove diameter racross the bottoms of `the grooves is .308 in., the

p idd Patented Aug. `li3, 1963 v 2 n through the barrel by the firing of a propulsive charge, the engagement of the helical lands With the material of the bullet imparts ltothe latter rotating motion necessary' to stabilize it in flight, and the function of the rifle is to impart to the projectle the. minimum rotational velocity 1 necessary for this stabilization. As is understood, the only portion of therifiing Which'significantly effects thisrota-` g tion is one side or the driving` side of each of the lands in the 'bore of the barrel, andit is the general experience that with 4 or groove rifiing, as is commonlyemployed in a .30 icaliber rifle, the minimum depth of groove must be approximately .004 in. to form a minimum driving land side of .004- in. Which is required for reliable engagement of the bullet hy the land to imp art the necessary spin to the bullet. Attempts to reduce manuiacturing costs bydecreasing the number of grooves or decreasing the depth of grooves to shortenthe machining time, have resulted in bar-reis `Which do not engage the projectile over a sufiicient area, and the result is a consequent failureto impart the necessary rotational velocity to the bullet." i

The effective driving area of the side of the lands Working on a projectile may be roughly computed as the land r side'heightmultiplied hy the length of the engagement of the land With `the projectile and multiplied by the number i bore of the barrel anumber ofv times to complete the average :being approximately .304 in. The cutting tool Which is passed through the -b arrel removes a small amount of this metal ateach pass, the amount removed being approahnately fifls in. This means that it -would `require eight passes ofthe tool to make a cut of adepth of .004 in., and thus require eight passes for` each of the grooves or 3 2 passes ofthe tool 'for :a harrel having four rifiing grooves. This requires a considerable length of time,

'in some instances up to 20 or 25 minutes, to cut the grooves in onebarrel. i

In some instances it has beenproposed to shorten the time required for providing the rilling ina b-arrel by the use `of a hroaching tool having multiple' 'cutting points Which Will form the -gr-oove with one pass of the tool. This toolisprovided with a number oftcircular lands of successively larger size and appropriately notched to give the groove-land Width relationship, the lands between the notches 'being arranged behind each other helically upon the broach With the appropriate helix angle requined -for rifling. Such` tools, although giving more rapid machining time for a finished harrel, :are prone to shatter and are co'stly to iabricate 'and keep in condition for use. Furthermore, in smaller 'bo-re guns, such as .ZZand .25 caliber, provision of adequate clearance `for the metal removed in the one or sometimes two broach passes makes for a Weak and generally unreliable tool. Furthermore, any one of the large number of individual cutting faces of the breach may at any time dull and consequently scratch or score the groove in which the land is cutting. p z

When bullets of appropriate size, which :are approxiof lands in the bore. H Thus, if in a .36 caliber barrel we assume a` land engagement With the projectile -for a length of /2 inch, the efiective engaging :area of all of the lands with the projectile Will be .004 times .5 times the number of grooves (either 4 `or 6) provided in the rbarrel. lt will be seen, therefore, that the area of engagement in a .30 caliber firearm would be from .008 to .012 sq. inches depending upon Whether 4 or 6 grooves are provided.

. It Will also :be seen that if the groove is made of a depth of .004 in. in a .30 caliber barrel, the groove` depth Will be approximately or more of the bore diameter of the harrel and the groove :depth is :always greater than A i ofthi-s diameter.` I-f it is attempted` to reduce the depth of the grocve in order to 'shorten the manufacturing time mately the groove diameter of the barrel, are forced required to make the barrel below this figure, fiaulty engagement of the rifiing lands with the projectile `results and a consequent failure to give the projectile the desired spin;

`Atternpts to countenact the reduction inthe depth 'of the groove by increasing the number of `grooves to give more driving land sides also prevents .any increase in eficiency in production because the total number of grooves must he increased correspond-ingly to the reduction in depth. Furthermore,`with an increased number of grooves to .be cut in, a b'arrel, the mechanical requirements for production equipment become so :complex as to render the increase in the number ofgrooves cut atpractioal impossibility with existing machinery beyond relatively low numbers of grooves; r

According to the present invention the `grooves are provided by a cold swedging method in that a tool having helical-r'ibs thereon is forced through the barrel, the tool r displac-ing the ,metal to form the grooves. The number of swedgng ribs provided on the tool is thesame as the number of rilling grooves provided* in the bore of the finished barrel, and it is only necessary for this swedge or button to make one pass to complete the rifiing operation so that the rifling time according to the present invention is 2 to 5 seconds per barrel as compared 'with the much longer time noted above in 'the usual rifiing operation.

improved obturation of the bore.

' increased:ac'cura cy in action. v v

Toi these and other ends the invention consists in the In swedging operation of the present invention, I provide a' much greater number of rifling grooves that has heretofore been the practice and swedge these grooves to amuch' lesser depth. The number of grooves may, of course, vary, but I have found that 16 of these comparatively minute grooves give good performance in the firearm having a barrel so made. Moreover,

V the depth ofthe grooves is approximately .0015 as cornpar'ed with the grooves having a depth of .004 astis the usual practice. The bore diameter isenlarged to maintain the same or greater effective cross section as compared I with common' practice. 'In other words, the barrelof a v ;30 cal iber gun according to the'present invention would have a bore diameter across the lands between .the grooves i of1304 in. and a groove diameter :across the bottoms of the grooves of `.307, the average 'being .3055 in.

One' of the :advantages of this rifling is the bore cross relatively. large numberof 'relatively shallow g'rooves in the bore 'of the barrel. i

Still another object ,of the invention is to provide a riflebarrel having improved nifiing thereby giving the gun novel features and combinations of parts .tot be hereinafter described and claimed;

In 'the accompanying drawings: g FIG. l is a side elevation al view :of a, riflebarrel embodying myl invention; v

FIG. 2 is 'a cross sectionalview of the barrel showing my improved -ifiing;

[FIG. 3 is asectional view of -a' gun barrel provided with' Conventional v rifling; 2 4

FIG. 4 is -an enlarged sectional view of the barrel showi in'gthe particular formation of the rifling gro oves formed n EFIG; 5 'is a side elevational view .of the swedge or button, 'usedrto-effect therifiing operation; and i FIG. 16 is a crosS-sectional view ofthe button I have shown in the drawingsa rifle 'barrel having the usual bore 11. It Wi-ll.be noted from the sectional view .shown in FIG. 2. that the barrel contains a large number of relatively minute rifl ing grooves 12 which, as is usual, arejformed helicallyabout the barrel boreso as to give the 'projeotile a ,twisting or rotating movement about its v axis. These grooves, :as will be more'fully explained hereinafter, are preferably formed by a swedging operation. Lands 13 are provided between the grooves', having land sides 14 to engage the bullet.

' The; tool employed 'for forming the grooves is shown in FIGS; '5 and 6 and consists of a swedge or button 15 so mounted that it may be forced through the bore of the gun with considerable' pressure. Provided on the button 15 are a plurality of helical grooves 16, defining lands 17 on the .button whichform the grooves in the bore of the barrel by plastic flow of the metal. These lands 17 are of such dimensions that ra diameter across two opposed grooves in the barrel formed by these Will `be approximately .307 in'. for .30 caliber ifles and are of sufiicient 'height so that the bottoms :of the grooves 16 between them will not foul the lands formed in the gun barrel. As

show-n, there are 16 of these lands formed on the swedge' 15 -so'as to form 16 grooves in the bore of the gun at one r pass of the swedge. As stated above, in a .30 caliber rifle,

v the grooves will preferably besubstantially .0015 inch in a plastic deformationof. the metal of the barrel'to form a 2 depth. It may also' be noted that the front end 18 of the swedge member is tapered so as to provide for its easy entrance into the bore of the barrel.

` A very important feature, as may be noted from the i cnlarged view of FIG. 4, is that the land sides 14 of the rifing grooves 12 are not in a nadial plane passing through the axis of the bore, but are inclinecl or at an angle to such a plane, and this angle is so chosen as to produce a maximum effect on the bullet. It may be assumed that the rifiing is so'directed as to effect a clockwise rotation of the bullet, as seen .in FIG. 4.

The radius of 'gyration of a solid body of generally cylindrical shape may be consideredto be R/x/where Ris the radius' of vthe body. The lands :arefsoformed that an element of the sides of the lands, if -projectecL as shown at '21, is tangent to a circle. 23 whose radius is R/x/ (Rbeing equal to one half of the' bore diameter of the barrel) and whose center is at the center-"of the bore. Therefore,rif thesecond tangent 22 be dnawn from 'the land side 14 to this circle, it Will be found that this line is substantially perpendicular to the side wall of -the rilling groove; This side of the land will, therefore, have amaxi f mum efect in inducing a rotative motion in the bullet in that it will 'act at the proper angle in the bullet' material the bullet to produce a much more ec'onomically than has been the case with l usual cutting or planing tool and in much less timefthus producing an improved weapon at a reduced cost. i

Rifling grooves have' been previously formed in gun barrels'by a swedging process but these grooves have been r of the normal depth, that is a depth of or more of r the bore diameter, and it `has=be`ennecessary to perform To illustrate a preferred embodiment' of my invention subsequent Operations upon the gun barrel 'to eliminate theundesirable'eife'ctsofthefswedging process. For ex r ample; when a swedging' tool has sufficiently high ridges upon it as' to form (grooves of thedepth referredto, there rid'ge into the groove has ragged fins 'Which proj ect inwardly toward the bore center and *which must beremoved to provide a uniform cross section throughout the length of the bore. v

Again most ,rifle barrels are tapered, the wall thickness being greater adjacent the breech than at'the muzzle, i The action of the swedging tool deforms to someextent the entire cross section of the barrel wall, and the amount of the permanent set or deformation in the Wall of the barrel is principally determined by the Wall thickness. In the event that the wall thickness is relatively small, the entire barrel' wall may be plastically deformed with the result that, afterthe' swedgehas passed, the bore is somewhat enlarged 'over its conditions prior to'the swedging 'operation, g As the swedge progressesj toward the' the barrel from 'the muzzle toward the breech. That is,`

both bore' and g'oove diameter of the barrel may be found to be greater at the muzzle than at the breech, where, if the Wall thickness is sufficiently high, the outer provision of a' large l ayers of the barrel wall arernot stretched beyond their elastic limit and'there is, therefore, little `or no plastic deformation of these outer layers. r

V :The taper thus formed in'the gun enlarging toward to-` ward the muzzle is very injur-ious to accuracy and to reasonable barre] life for the bullet is free to oscillate laterally in the bore adjacent the muzzle, thus disturbing its guided motion and permitting gasesto escape by the bullet which injure the barrelby erosion. Moreover, it

is not practical to remedy this difiiculty by iin-ish rifling the bore of the barrel while the latter is in its unturned or cylindrical condition asfthe turning of the gun barrel to the final desired taperrproduces some distortion of the barrel and consequent deviation of the bore axis which requires starightening. After rilling,` the former smooth cylindrical bore surface isdisturbed by the rifling so that reasonable straightening of the rifle cannot be reliably effected; Therefore, the remedial Operations necessary to counteract the disturbances produced .by the swedging 4 of grooves of normal depth substantially increases the overall costof the product as well as 'giving dubious ,performance in the finished product.

The swedging tool which I employ is preferably formed by nachining or grinding Operations, and the grooves in the swedge which definethe lands of the finished bar-` rel are of sufficient depth so that in the swedging of the barrel the metal of the face of the lands beingformed does not in genenal engage with the bottom of the groove in the swedging tool. Therefore, the deep stresses which might otherwise be effected in the metal of the barrel wall are eliminated by the elimination of direct contact with or any cold working of the land surfaces of the bore. The actual volume of the metal displaced by the passage of the swedging tool is substantially less than that which has been previously required in forming grooves of normal depth by swedging Operations with a result that deep underlying stresses are not produced.

As previously stated, I have foundthat 16 of these comparatively minute grooves having a` depth of approximately .001 to .0015 in. in a .30`caliber barrel give excellent performance in the firearm so made. The

groove depth of such a :barrel made according to the present invention would be or less of the bore diameter in contrast to thegroove 'depth of or more of the bore diameter as *found in `barrels having conven- V tional riiiing. Moreover, it will be found that when the' land'side 'of each of the grooves has a height dimension of from .00 1 to .0015 in., the land area which is effective in prod-ucing the rotatiorial spin of the projectile is'approximately the same as that of barrels having four to r six grooves 'of a depth of .004 in., for if we multiply this groove depth of -.0Ol in'. totG015 in. times .`5 inch (the length of engagement) times 16, we arrive at a product 'of .008 sq. in. to` .012 sq. in., as was found to be the case in the Conventional .30 caliber gun.

land so that .it is normal or toe circle constructed `about the center of thebarrel with ,the radius equal to the radius of gyration ofthe h projectile so ?that the full rotational th ust ofthe land 'is deliventd most efficiently to the projectile to eifectrotation without `distortion `of or cutting of the projectile.

is shown in FIG. 4. whe'e itmay be considered the spin given to the :projectile is in' a clockwise direction, :and it will .be seen that anelernent of the surface 14 lies its respective land side of approximately 90 degrees plus Also I provide additional security of engagement of U the lands with the projectile by virtue of the shape of the lands formed in the barrel. In conventional barrels the land side of each land which engages the projectile is formed by a cutter having two parallel sides such that the Opposing faces of two adjacent lands formed by the cutter lie in parallel planes on chords of the bore substantially parallel to a diameter through the center of the adjacent groove. This is shown in FIG. 3 of the drawings r `where the sides 25 of the lands 26 are substantially parallel to the diameter of the bore 27 passing through the center of the groove 28. `The angle at which the land sides engage the projectile will, therefore, in accordance with the width of the individual groov'es and `the number of the grooves formed in the barrel. T hey furthermore engage the projectile in such fashion that the driving surface tends to cut away from or disengage the material of the projectile, thus throwing up pronounced burrs on the latter.

As opposed to this, I form thedriving side of each on the tangent '2,1 to the'circle `'23 andis perpendicular to the tangent 22. Thecenter of the `circle23` isat the center of rthebore, and itsradius is equal to the radius of gyration of the hullet. 4 r

` A further advantage of the present invention lies in the relatively low height of the lands ordepths of the grooves. travel from the lands to` the metal of the baneLthe distance being -only approximately onefourth as great as that with the normal depth of groove. Burthermore, the :inner surface or top of the land joinsuthe land side :at an angle of approximattly 135 degrees (the land itself making an angle of approximately 135 degreeswith a radial line drawn thereto) so that these corners are net" so sharp as the substantially 90-degree corners provided in the `usualnifiing,-and there are no isolated zones in the lands exposed on two sides to heat 'through substantial areas working on asmalilrn-ass. The bore surface and particularly the land mass will, therefore, be cooler dur-` projectile so that there is no gas leakage by the bullet Gasleakage is further preand no resultant erosion. vented by the wedging action ofthe land as it engages the bullet. Since rtheland has an included angleb'etween the arc' angle `of the land subtended at the bore' axis, the landwill morevuniformly engage the projectile `over its .entire surface as 'compared with co nvenrtional lands which have parallel sides.

Anotherwsu bstantial improvement in 'a gun manufacuured according to the present invention is that the projectile is engaged securely by the lands with maximum efliciency' and without the deep localized distortion of the` projectile eifected by the'higher lands of abarrel having conventional rilling. i Such distortion effects are reduced `by approximately one fourth, and a substantial gain in accuracy is achieved. Moreover, an improvement in the surface finish of the working portion of the bore is obtained in that the iand sides ware not ragged as is usually the case.` In the present instance the ribs on the swedgingtool having an included angle between their faces of 90 degrees plus the subtended arc engle burnish the metal to a high finish not only` on the bottoms of the grooves hut also on the driving side or vital working portion i 'of the land. This is in contnast to the commonpractice wherein the land side is formed by shearing action. r r

While I have shown and described a preferred embodiment of my invention, it will be understood that it is c not to be limited to all of the details shown or the steps described, but isoapble of modification and variation within the spirit of the invention and within the scope of 'the claims. h What I claim is: r 1. A gun barrel provided with a plurality of helically `disposed rilling grooves in 'the bore thereof with lands between the grooves, there being at least 5 of such grooves for every inch of bore diameter, and the driving side perpendicular to a tangent This provides a short path for the heat to v 4 of ?'ech of `aid lands being disposed subtrti allytarigen tiall-y t'o a circle having a center at the bore axis and a 'fionoif theborei-f, g V -2uA gun barrel provided with a plurality ,of helically b di'spoed rifiing 'grdoy e's in "the bore thereof with'lnds between the-g 'roove`s, there being at least ten of 'Such V i groo's e'sg'and the 'driving side of each of said lands ,being 'disposed substantially taigentially to a circle having a' center at the bore axisand a 'radius equal mo the radius 1 1 2, 11 7- `1,-. z 5

of gyration of a n ic l Sectionof the bore. s v 1 z 1 V V OTHER ,REFERE'N ?The Modern Gunsmh' b J. V. we',"vo1. I I,-Fuik A, V and Wagnaus Co., New York, copyright'1937, pages 

1. A GUN BARREL PROVIDED WITH A PLURALITY OF HELICALLY DISPOSED RIFLING GROOVES IN THE BORE THEREOF WITH LANDS BETWEEN THE GROOVES, THERE BEING AT LEAST 5 OF SUCH GROOVES FOR EVERY 1/10 INCH OF BORE DIAMETER, AND THE DRIVING SIDE OF EACH OF SAID LANDS BEING DISPOSED SUBSTANTIALLY TANGENTIALLY TO A CIRCLE HAVING A CENTER AT THE BORE AXIS AND A RADIUS EQUAL TO THE RADIUS OF GYRATION OF A CYLINDRICAL SECTION OF THE BORE. 